import { addLeadingZeros } from "../../addLeadingZeros/index.ts";

/*
 * |     | Unit                           |     | Unit                           |
 * |-----|--------------------------------|-----|--------------------------------|
 * |  a  | AM, PM                         |  A* |                                |
 * |  d  | Day of month                   |  D  |                                |
 * |  h  | Hour [1-12]                    |  H  | Hour [0-23]                    |
 * |  m  | Minute                         |  M  | Month                          |
 * |  s  | Second                         |  S  | Fraction of second             |
 * |  y  | Year (abs)                     |  Y  |                                |
 *
 * Letters marked by * are not implemented but reserved by Unicode standard.
 */

export const lightFormatters = {
  // Year
  y(date: Date, token: string): string {
    // From http://www.unicode.org/reports/tr35/tr35-31/tr35-dates.html#Date_Format_tokens
    // | Year     |     y | yy |   yyy |  yyyy | yyyyy |
    // |----------|-------|----|-------|-------|-------|
    // | AD 1     |     1 | 01 |   001 |  0001 | 00001 |
    // | AD 12    |    12 | 12 |   012 |  0012 | 00012 |
    // | AD 123   |   123 | 23 |   123 |  0123 | 00123 |
    // | AD 1234  |  1234 | 34 |  1234 |  1234 | 01234 |
    // | AD 12345 | 12345 | 45 | 12345 | 12345 | 12345 |

    const signedYear = date.getFullYear();
    // Returns 1 for 1 BC (which is year 0 in JavaScript)
    const year = signedYear > 0 ? signedYear : 1 - signedYear;
    return addLeadingZeros(token === "yy" ? year % 100 : year, token.length);
  },

  // Month
  M(date: Date, token: string): string {
    const month = date.getMonth();
    return token === "M" ? String(month + 1) : addLeadingZeros(month + 1, 2);
  },

  // Day of the month
  d(date: Date, token: string): string {
    return addLeadingZeros(date.getDate(), token.length);
  },

  // AM or PM
  a(date: Date, token: string): string {
    const dayPeriodEnumValue = date.getHours() / 12 >= 1 ? "pm" : "am";

    switch (token) {
      case "a":
      case "aa":
        return dayPeriodEnumValue.toUpperCase();
      case "aaa":
        return dayPeriodEnumValue;
      case "aaaaa":
        return dayPeriodEnumValue[0];
      case "aaaa":
      default:
        return dayPeriodEnumValue === "am" ? "a.m." : "p.m.";
    }
  },

  // Hour [1-12]
  h(date: Date, token: string): string {
    return addLeadingZeros(date.getHours() % 12 || 12, token.length);
  },

  // Hour [0-23]
  H(date: Date, token: string): string {
    return addLeadingZeros(date.getHours(), token.length);
  },

  // Minute
  m(date: Date, token: string): string {
    return addLeadingZeros(date.getMinutes(), token.length);
  },

  // Second
  s(date: Date, token: string): string {
    return addLeadingZeros(date.getSeconds(), token.length);
  },

  // Fraction of second
  S(date: Date, token: string): string {
    const numberOfDigits = token.length;
    const milliseconds = date.getMilliseconds();
    const fractionalSeconds = Math.trunc(
      milliseconds * Math.pow(10, numberOfDigits - 3),
    );
    return addLeadingZeros(fractionalSeconds, token.length);
  },
};
